一个DX10创建纹理并修改纹理数据的问题？

ljlees0830

D3D10_TEXTURE2D_DESC desc;
        desc.Width = 256;
        desc.Height = 256;
        desc.MipLevels = 1;
        desc.ArraySize = 1;
        desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
        desc.SampleDesc.Count = 1;
        desc.SampleDesc.Quality = 0;
        desc.Usage = D3D10_USAGE_DYNAMIC;
        desc.BindFlags = D3D10_BIND_SHADER_RESOURCE;
        desc.CPUAccessFlags = D3D10_CPU_ACCESS_WRITE | D3D10_CPU_ACCESS_READ;
        desc.MiscFlags = 0;

        ID3D10Texture2D *pTexture = NULL;
        g_pd3dDevice->CreateTexture2D( &desc, NULL, &pTexture );

        // Create the shader-resource view
        D3D10_SHADER_RESOURCE_VIEW_DESC srDesc;
        srDesc.Format = desc.Format;
        srDesc.ViewDimension = D3D10_SRV_DIMENSION_TEXTURE2D;
        srDesc.Texture2D.MostDetailedMip = 0;
        srDesc.Texture2D.MipLevels = 1;

        ID3D10ShaderResourceView *pShaderResView = NULL;
        g_pd3dDevice->CreateShaderResourceView( pTexture, &srDesc, &pShaderResView );

        D3D10_MAPPED_TEXTURE2D mappedTex;
        pTexture->Map( D3D10CalcSubresource(0, 0, 1), D3D10_MAP_WRITE_DISCARD, 0, &mappedTex );

各位大牛，麻烦帮忙看一下，我按照微软官网上面的实例代码写的程序，为什么Map会出错呢？